This relates generally to semiconductor devices and processes, and more particularly to structures and fabrication of packaged semiconductor devices having patterned conductance dual-material nanoparticle layers.
Based on their functions, semiconductor packages include a variety of different materials. Metals formed as leadframes are employed for mechanical stability, and electrical and thermal conductance. Insulators, such as polymeric molding compounds, are used for encapsulations. In packaging fabrication, it is common practice to attach a plurality of semiconductor chips to a strip of leadframe (or packaging substrate), to connect the chips to their respective leads, and then to encapsulate the assembled chips in packages. Packages protect the enclosed parts against mechanical damage and environmental influences such as moisture and light. After the encapsulation step, the package chips are separated from the leadframe strip (or packaging substrate) into discrete units by a trimming and forming step.
Today's semiconductor technology employs a number of methods to raise the level of adhesion between the diversified materials so that the package passes accelerated tests and use conditions without delamination. Among the efforts are chemically purifying the molding compounds, activating leadframe metal surfaces (such as by plasma just before the molding process), and enhancing the affinity of leadframe metals to polymeric compounds by oxidizing the base metal. Furthermore, design features such as indentations, grooves or protrusions, overhangs and other three-dimensional features are added to the leadframe surface for improved interlocking with the package material.
Another example of known technology to increase adhesion between leadframe, chip, and encapsulation compound in semiconductor packages, is the roughening of the whole leadframe surface by chemically etching the leadframe surface after stamping or etching the pattern from a metal sheet. Chemical etching is a subtractive process using an etchant. Chemical etching creates a micro-crystalline metal surface.
Yet another known method to achieve a rough surface is the use of a specialized metal plating bath, such as a nickel plating bath, to deposit a rough metal (such as nickel) layer. This method is an additive process; the created surface roughness is on the order of 1 to 10 μm. Roughening of the leadframe surface may have some unwelcome side effects. General roughening of the surface impacts wire bonding negatively. For example, vision systems have trouble seeing the roughened surface, the rough surface shortens capillary life; and micro-contaminants on the rough surface degrade bonding consistency. General rough surfaces tend to allow more bleeding, when the resin component separates from the bulk of the chip attach compound and spreads over the surface of the chip pad. The resin bleed, in turn, can degrade moisture level sensitivity and interfere with down bonds on the chip pad.
The success of all these efforts has only been limited, especially because the adhesive effectiveness is diminishing ever more when another downscaling step of device miniaturization is implemented.